Process for producing high-pressure hydrogen and system for producing high-pressure hydrogen

ABSTRACT

To produce high-pressure hydrogen, water and a hydrogen-generating material (MgH 2 ) which reacts with water to generate hydrogen are weighed so that a target high hydrogen pressure is generated in a high-pressure container. Then, the hydrogen-generating material is introduced into the high-pressure container through its supply port, and water is introduced into the high-pressure container through the supply port. Thereafter, the supply port is closed, thereby causing a reaction between the hydrogen-generating material and the water, so that the hydrogen pressure in the high-pressure container reaches a target high hydrogen pressure.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a process for producinghigh-pressure hydrogen, and a system for producing high-pressurehydrogen.

[0003] 2. Description of the Related Art

[0004] To produce high-pressure hydrogen, a measure is conventionallyemployed, which comprises the steps of generating hydrogen having apressure of about 0.008 to 3.2 MPa in a hydrogen generator, pressurizingthe hydrogen from the hydrogen generator by a high-pressure compressor,and filling it into a hydrogen-storing vessel (see Japanese PatentApplication Laid-open Nos. 9-266006 and 11-283633).

[0005] However, the high-pressure compressor generally has a lowcompression efficiency, and hence a great deal of energy isuneconomically required for obtaining high-pressure hydrogen.

SUMMARY OF THE INVENTION

[0006] Accordingly, it is an object of the present invention to providean economical high-pressure hydrogen producing process capable ofproducing high-pressure hydrogen at a low cost by employing a verysimple method.

[0007] To achieve the above object, according to the present invention,there is provided a process for producing high-pressure hydrogen,comprising the steps of: weighing water and a hydrogen-generatingmaterial which reacts with water to generate hydrogen so that a targethigh hydrogen pressure is generated in a high-pressure container;introducing said hydrogen-generating material and said water into saidhigh-pressure container through its supply port; and closing said supplyport, thereby causing a reaction between said hydrogen-generatingmaterial and said water, so that a hydrogen pressure generated in saidhigh-pressure container reaches said target high hydrogen pressure.

[0008] With the above-described process, high-pressure hydrogen can beproduced at a low cost by such a very simple method that thehydrogen-generating material and the water are weighed and introducedinto the high-pressure container.

[0009] The hydrogen pressure achieved by the reaction between thehydrogen-generating material and the water depends on an amount ofhydrogen generated at a reached temperature of the reaction, and isdetermined in an equilibrium theory. In general, an amount of hydrogengenerated by the hydrogen-generating material which is highly active towater at about ambient temperature, does not greatly rely on thepressure in the container, and hence the hydrogen pressure reaches apressure determined in the equilibrium theory. However, if the pressurein the container is sufficiently high during the reaction and anequilibrium reaction does not advantage, the hydrogen pressure does notreach a chemical stoichiometric pressure and is constant at anequilibrium pressure, and hence the unreacted hydrogen-generatingmaterial remains. Namely, the pressure in the container is kept constantuntil all the unreacted hydrogen-generating material reacts.

[0010] It is another object of the present invention to provide ahigh-pressure hydrogen producing system which is capable of producinghigh-pressure hydrogen at a low cost.

[0011] To achieve the above object, according to the present invention,there is provided a system for producing high-pressure hydrogen,comprising: a hydrogen generator into which water and ahydrogen-generating material which reacts with water to generatehydrogen are introduced, said hydrogen-generating material and saidwater being weighed so that hydrogen having a target high pressure isproduced; a hydrogen-storing vessel for storing a high-pressure hydrogengenerated by said hydrogen generator; and a connecting member adapted toconnect said hydrogen generator and said hydrogen-storing vessel to eachother in a course of filling said hydrogen-storing vessel with thehigh-pressure hydrogen and adapted to disconnect said hydrogen generatorand said hydrogen-storing vessel from each other after saidhydrogen-storing vessel is filled with the high-pressure hydrogen.

[0012] With the above-described system, the high-pressure hydrogen canbe generated at a low cost by such a very simple method of weighing thehydrogen-generating material and the water and introducing them into thehydrogen generator. In addition, the hydrogen-storing vessel can befilled with the high-pressure hydrogen by connecting the hydrogengenerator to the hydrogen-storing vessel through the connecting member,whereby the high-pressure hydrogen can be stored in the hydrogen-storingvessel. After the hydrogen-storing vessel is filled with thehigh-pressure hydrogen, the hydrogen generator is disconnected from thehydrogen-storing vessel. Therefore, when the hydrogen-storing vessel istransported or mounted on, for example, a vehicle including a fuel cell,there is obtained an advance in reducing the weight, because the weightof the hydrogen generator and the weight of a reaction product derivedfrom the hydrogen-generating material and the water are eliminated.

[0013] The above and other objects, features and advantages of theinvention will become apparent from the following description of thepreferred embodiment taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a diagram showing the connection between a high-pressurecontainer and a fuel cell;

[0015]FIG. 2 is an enlarged sectional view of essential portions of thehigh-pressure container;

[0016]FIG. 3 is a diagram showing a state in which a hydrogen-generatingmaterial is introduced into the high-pressure container;

[0017]FIG. 4 is a diagram showing a state in which water is introducedinto the high-pressure container;

[0018]FIG. 5 is a diagram for explaining Mg alloy particles;

[0019]FIG. 6 is a graph showing the relationship between the elapsedtime and the hydrogen pressure in the high-pressure container;

[0020]FIG. 7 is a front view of a high-pressure hydrogen producingsystem in a state in which a hydrogen-storing vessel and a hydrogengenerator are disconnected from each other before introduction ofhydrogen into the hydrogen-storing vessel;

[0021]FIG. 8 is an enlarged view of essential portions of FIG. 7;

[0022]FIG. 9 is a front view of the high-pressure hydrogen producingsystem in a state in which the hydrogen-storing vessel and the hydrogengenerator are connected to each other, and hydrogen is being introducedinto the hydrogen-storing vessel;

[0023]FIG. 10 is an enlarged view of essential portions of FIG. 9;

[0024]FIG. 11 is a front view of the high-pressure hydrogen producingsystem in a state in which the hydrogen-storing vessel and the hydrogengenerator are disconnected from each other after filling thehydrogen-storing vessel with high-pressure hydrogen;

[0025]FIG. 12 is a graph of one example of the relationship between theelapsed time and the hydrogen pressure in a spherical body;

[0026]FIG. 13 is a graph of another example of the relationship betweenthe elapsed time and the hydrogen pressure in the spherical body.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] (Embodiment I)

[0028] Referring to FIG. 1, a high-pressure container 1 is mounted on avehicle and includes a container body 2 which has a cylindrical portion3 and bowl-shaped end wall portions 4 and 5 connected to opposite endsof the cylindrical portion 3, respectively. A first connecting portion 7having a supply port 6 protrudes from the bowl-shaped end wall portion4, and a second connecting portion 9 having a discharge port 8 protrudesfrom the bowl-shaped end wall portion 5. A first pipe 11 having anon-off valve 10 is connected to the first connecting portion 7. Thesecond connecting portion 9 is connected to a fuel cell 13 through asecond pipe 12. A pressure-reducing device 14 having an on-off valve ismounted in the second pipe 12. As shown in FIG. 2, the container body 2comprises an outer shell 15 made of a carbon composite material, and aliner 16 made of a high-density polyethylene and covering the entireinner surface of the outer shell 15.

[0029] If the on-off valve of the pressure-reducing device 14 is openedat the start of the operation of the fuel cell 13 in a state in whichhigh-pressure hydrogen is filled in the high-pressure container 1,high-pressure hydrogen is supplied to the fuel cell 13 after reductionof the pressure thereof.

[0030] To produce high-pressure hydrogen, a powdery hydrogen-generatingmaterial which reacts with water to generate hydrogen and water arefirst weighed so that a target high hydrogen pressure is produced in thehigh-pressure container 1. Then, as shown in FIG. 3, the weighed powderyhydrogen-generating material 17 is placed into the high-pressurecontainer 1 through the supply port 6 in a state in which the first pipe11 is removed from the first connecting portion 7. Further, as shown inFIG. 4, the first pipe 11 is connected to the first connecting portion7, and the weighed water is placed into the high-pressure container 1through the supply port 6 in a state in which the on-off valve of thepressure-reducing device 14 is closed. Thereafter, the supply port 6 isclosed by closing the on-off valve 10, whereby the hydrogen pressure inthe high-pressure container 1 is increased to reach the target highhydrogen pressure by the reaction between the powderyhydrogen-generating material 17 and the water.

[0031] The powdery hydrogen-generating material 17 which may be used isan aggregate comprising at least one of Mg particles and hydrogenated Mg(MgH₂) particles, namely, an Mg powder, a hydrogenated Mg powder, or amixture of an Mg powder and a hydrogenated Mg powder.

[0032] A hydrogenated Mg alloy powder may be also used as thehydrogen-generating material 17. The hydrogenated Mg alloy powder is apowder produced by hydrogenating an aggregate of Mg alloy particles 20comprising Mg particles 18, and a plurality of catalyst metal fineparticles 19 existing on a surface of each of the Mg particles 18 andwithin each of the Mg particles 18. The catalyst metal fine particles 19is at least one selected from among Ni fine particles, Ni alloy fineparticles, Fe fine particles, Fe alloy fine particles, V fine particles,V alloy fine particles, Mn fine particles, Mn alloy fine particles, Tifine particles, Ti alloy fine particles, Cu fine particles, Cu alloyfine particles, Ag fine particles, Ag alloy fine particles, Ca fineparticles, Ca alloy fine particles, Zn fine particles, Zn alloy fineparticles, Zr fine particles, Zr alloy fine particles, Co fineparticles, Co alloy fine particles, Cr fine particles, Cr alloy fineparticles, Al fine particles and Al alloy fine particles.

[0033] The content G of the catalyst metal fine particles 19 in the Mgalloy powder is set in a range of 0.1% by atom≦G≦5.0% by atom. If thecontent G is lower than 0.1% by atom, no effect is provided by theaddition. On the other hand, if the content G is higher than 5.0% byatom, the amount of hydrogen generated is reduced, resulting in nopracticality. The content G of the catalyst metal fine particles 19 ispreferably in a range of 0.3% by atom≦G≦1.0% by atom. The Mg alloypowder is produced by mechanical alloying, and hence it is appropriatethat the particle size D of the Mg particles 18 is in a range of 1μm≦D≦500 μm, and the particle size d of the catalyst metal fineparticles 19 is in a range of 10 nm≦d≦500 nm. In this case, the particlesizes D and d are defined as the longest one (largest diameter) ofdiameters in each of the Mg particles, etc. in a microphotograph.

EXAMPLE OF PRODUCTION OF HIGH-PRESSURE HYDROGEN

[0034] High-pressure container 1: the inner diameter is 200 mm; thetower length is 800 mm; the volume is about 100 liters; and a targethydrogen pressure is 27 MPa. Hydrogen-generating material 17: an alloypowder has a composition of Mg_(99.5)Ni_(0.5) (unit of numerical valueis % by atom); a particle size D of Mg particles 18 is in a range of 2μm≦D≦300 μm; a particle size d of Ni particles is in a range of 10nm≦d≦200 nm; the supply amount is 15 kg. Water: an ion-exchanged waterat 40° C. supplied in an amount of 25 liters.

[0035] A line a in FIG. 6 shows a change with time in hydrogen pressureproduced by a reaction between the alloy powder and the water in thehigh-pressure container 1, namely, MgH₂+2H₂O→Mg(OH)₂+2H₂. A line b inFIG. 6 corresponds to a case where hydrogen was filled in thehigh-pressure container 1 by a high-pressure compressor. As apparentfrom the line a in FIG. 6, a high hydrogen pressure equivalent to thatwhen the high-pressure compressor is used, can be produced without useof the high-pressure compressor by using the hydrogen-generatingmaterial and the water as described above.

[0036] Mg(OH)₂ remaining in the high-pressure container 1 is dischargedfrom the supply port 6, and the recovery of Mg is carried out.

[0037] As can be seen from FIG. 6, a hydrogen pressure of about 10 MPain the high-pressure container 1 suffices to operate the fuel cell 13 inorder to cause the vehicle to travel. Therefore, the vehicle can bestarted within a very short time such as about 2 minutes afterintroduction of water into the high-pressure container 1. Thereafter,the generation of hydrogen is continued until the hydrogen-generatingmaterial is used up, and hence the traveling of the vehicle is conductedwithout any problem.

[0038] If the high-pressure compressor is used, the vehicle cannot bestarted before the filling of hydrogen into the high-pressure containeris finished. Namely, the filling of hydrogen is not finished unlessabout 10 minutes is elapsed from the start of the filling of hydrogen inthe line b in FIG. 6, and hence the driver must wait a time to start thevehicle, before the filling of hydrogen is finished.

[0039] In order to shorten the hydrogen-filling time, there is conceiveda process for filling hydrogen into the high-pressure container 1mounted on the vehicle, which can be considered is a measure whichcomprises filling hydrogen into a buffer tank by a high-pressurecompressor in a hydrogen station and transferring the high-pressurehydrogen in the buffer tank into the high-pressure container mounted onthe vehicle. In this case, however, the hydrogen pressure in the buffertank must be larger than that in the high-pressure container 1, andhence a great deal of energy is required for filling hydrogen into thebuffer tank. In addition, a cascade-type filling system comprising aplurality of buffer tanks entails disadvantages such as an increase insize of the system and an increase in area for installation of thesystem. According to the present invention, all these problems areeliminated.

[0040] (Embodiment II)

[0041] Referring to FIGS. 7 and 8, a high-pressure producing system 21includes a hydrogen generator 22, a hydrogen-storing vessel 23, and aconnecting member 24 adapted to connect and disconnect the hydrogengenerator 22 and the hydrogen-storing vessel 23 to and from each other.The hydrogen generator 22 has a spherical body 25, which is providedwith a first half 26 of the connecting member 24, a water-introducingpipe 28 having an on-off valve 27, and a pressure indicator 29. Thehydrogen-storing vessel 23 has a spherical body 30 having a diameterlarger than that of the spherical body 25 of the hydrogen generator 22.The spherical body 30 is provided with a second half 31 of theconnecting member 24, a hydrogen discharge pipe 33 having an on-offvalve 32, and a pressure indicator 34.

[0042] A hydrogen-generating material which reacts with water togenerate hydrogen and the water are weighed and introduced into thespherical body 25 of the hydrogen generator 22 so that a targethigh-pressure hydrogen is generated. Example of the hydrogen-generatingmaterial, which may be used, are at least one powder or granularmaterial of metal selected from among NaH, Na, NaBH₄, MgH₂, Mg,Mg(BH₄)₂, Mg(AlH₄)₂, LiH, LiAlH₄, LiBH₄, Li, K, Ca, Sr and Be. Thehydrogen-generating material is introduced into the spherical body 25 byopening a regularly-closed valve (not shown) mounted in a cylindricalmain body 35 of the first half 26, and thereafter the regularly-closedvalve is automatically closed. On the other hand, the water isintroduced into the spherical body 25 through the water-introducing pipe28 by opening the on-off valve 27 and thereafter, the on-off valve 27 isclosed.

[0043] Thus, hydrogen is generated in the spherical body 25. It isdesirable that the spherical body 25 is cooled during generation ofhydrogen.

[0044] In the hydrogen-storing vessel 23, the second half 31 of theconnecting member 24 includes a cylindrical main body 36, and anoperating lever 37 mounted on an outer surface of the main body 36. Whenthe operating lever 37 is in one of positions in which its axisintersects an axis of the cylindrical main body 36, e.g., a firstposition A on the left of the cylindrical main body 36 as shown in FIGS.7 and 8, an on-off valve (not shown) in the cylindrical main body 36 isin a state in which it is closed and cannot be connected to the firsthalf 26. On the other hand, when the operating lever 37 is turned in acounterclockwise direction from the first position A and retained in theother position in which its axis intersects an axis of the cylindricalmain body 36, namely, in a second position B on the right of thecylindrical main body 36 in FIGS. 9 and 10 in a state in which thecylindrical main body 35 of the first half 26 has been fitted into thecylindrical main body 36 of the second half 31, the first half 26 isconnected to the second half 31, and the regularly-closed valve and theon-off valve in the cylindrical main bodies 35 and 36 are opened,whereby the spherical bodies 25 and 30 are put into communication witheach other.

[0045] Thus, hydrogen is introduced from inside the spherical body 25 ofthe hydrogen generator 22 into the spherical body 30 of thehydrogen-storing vessel 23, whereby the interior of the spherical body30 is filled with the high-pressure hydrogen.

[0046] When the operating lever 37 located in the second position B inFIGS. 9 and 10 is turned in a clockwise direction and retained in thefirst position A as shown in FIG. 11, the hydrogen generator 22 isdisconnected from the hydrogen-storing vessel 23, whereby thehigh-pressure hydrogen is stored in the spherical body 30 of thehydrogen-storing vessel 23, and the regularly-closed valve of the firsthalf 26 and the on-off valve of the second half 31 are closed.

[0047] In this way, after the interior of the spherical body 30 of thehydrogen-storing vessel 23 is filled with the high-pressure hydrogen,the hydrogen generator 22 is disconnected from the hydrogen-storingvessel 23. Therefore, when the hydrogen-storing vessel 23 is mounted,for example, on a vehicle including a fuel cell, there is obtained anadvantage in reducing the weight, because the weight of the hydrogengenerator 22 and the weight of a reaction product derived from thehydrogen-generating material and the water are eliminated.

[0048] The reaction product derived from the water and thehydrogen-generating material is discharged out of the spherical body 25through the cylindrical main body 35 of the first half 26.

Example 1 of Production of High-Pressure Hydrogen

[0049] A powder of MgH₂ was introduced in an amount of 100 g into aspherical body 25 made of an Al alloy and having a volume of 300 cc inthe hydrogen generator 22, and water was introduced in an amount of 150cc into the spherical body 25. Thereafter, the hydrogen generator 22 wasconnected to the hydrogen-storing vessel 23 through the connectingmember 24. A chemical reaction represented by MgH₂+2H₂O→Mg(OH)₂+2H₂occurred within the spherical body 25 of the hydrogen generator 22 togenerate hydrogen. This hydrogen was introduced into a spherical body 30made of an Al alloy and having a volume of 1,000 cc in thehydrogen-storing vessel 23. After lapse of about 1 hour, the hydrogenpressure in the spherical body 30 reached 13 MPa, and when the hydrogenpressure did not rise further, the hydrogen generator 22 wasdisconnected from the hydrogen-storing vessel 23.

[0050] In this case, the total weight of the hydrogen-storing vessel 23including the weight of the high-pressure hydrogen in an amount of 1,000cc was 1,922 g, and the entire volume of the hydrogen-storing vessel 23was 1,704 cm³. For example, if an attempt is made to introduce a powderof MgH₂ and water in amounts equal to those described above into aspherical body 25 made of an Al alloy and having a volume of 1,300 cc ina hydrogen-storing vessel also serving as a hydrogen generator, tothereby produce high-pressure hydrogen of 13 MPa, the total weight ofthe hydrogen-storing vessel including the weights of the high-pressurehydrogen and a reaction product is 2,676 g, and the entire volume of thehydrogen-storing vessel is 2,216 cm³. Therefore, the meaning of thearrangement such that the hydrogen generator 22 is capable of beingdisconnected from the hydrogen-storing vessel 23 for the purpose ofreduction in weight, is obvious. In the chemical reaction, the reactionrate can be increased using a catalyst.

Example 2 of Production of High-Pressure Hydrogen

[0051] A granular material of NaH having a particle size in a range of1.0 to 5.0 mm was introduced in an amount of 290 g into a spherical body25 made of an Al alloy and having a volume of 1,000 cc in the hydrogengenerator 22, and ion-exchanged water at 40° C. was then introduced inan amount of 250 cc into the spherical body 25. Thus, a chemicalreaction represented by NaH+H₂O→NaOH+H₂ occurred to produce hydrogen. Inthis case, a catalyst is not required, because NaOH has a very highreactivity with water.

[0052] A change with time in hydrogen pressure in the spherical body 25was examined to provide a result indicated by a line XI in FIG. 12. InFIG. 12, a line X₂ indicates a case where a high-pressure compressor wasused.

[0053] As apparent from FIG. 12, a high-pressure hydrogen as in the casewhere the high-pressure compressor is used, can be produced by using thehydrogen generator 22.

Example 3 of Production of High-Pressure Hydrogen

[0054] A granular material of NaBH₄ having a particle size in a range of1.0 to 5.0 mm was introduced in an amount of 114 g into a spherical body25 made of an Al alloy and having a volume of 1,000 cc in the hydrogengenerator 22, and ion-exchanged water at 40° C. was then introduced inan amount of 250 cc into the spherical body 25. Thus, a chemicalreaction represented by NaBH₄+6H₂O→NaBO₂.4H₂O+4H₂ occurred to producehydrogen. In this case, a catalyst is not required, because NaBH₄ has avery high reactivity with water.

[0055] A change with time in hydrogen pressure in the spherical body 25was examined to provide a result indicated by a line Xi in FIG. 13. InFIG. 13, a line X₂ indicates a case where a high-pressure compressor wasused.

[0056] As apparent from FIG. 13, a high-pressure hydrogen as in the casewhere the high-pressure compressor is used can be produced by using thehydrogen generator 22.

[0057] Although the embodiments of the present invention have beendescribed in detail, it will be understood that the present invention isnot limited to the above-described embodiments, and variousmodifications in design may be made without departing from the spiritand scope of the invention defined in the claims.

What is claimed is:
 1. A process for producing high-pressure hydrogen,comprising the steps of: weighing water and a hydrogen-generatingmaterial which reacts with water to generate hydrogen so that a targethigh hydrogen pressure is generated in a high-pressure container;introducing said hydrogen-generating material and said water into saidhigh-pressure container through its supply port; and closing said supplyport, thereby causing a reaction between said hydrogen-generatingmaterial and said water, so that a hydrogen pressure generated in saidhigh-pressure container reaches said target high hydrogen pressure.
 2. Aprocess for producing high-pressure hydrogen according to claim 1,wherein said hydrogen-generating material is an aggregate comprising atleast one of Mg particles and hydrogenated Mg particles.
 3. A processfor producing high-pressure hydrogen according to claim 1, wherein saidhydrogen-generating material is a material produced by hydrogenating anaggregate of Mg alloy particles comprising Mg particles and a pluralityof catalyst metal fine particles existing on a surface of each of the Mgparticles and within each of the Mg particles, said catalyst metal fineparticles being at least one selected from among Ni fine particles, Nialloy fine particles, Fe fine particles, Fe alloy fine particles, V fineparticles, V alloy fine particles, Mn fine particles, Mn alloy fineparticles, Ti fine particles, Ti alloy fine particles, Cu fineparticles, Cu alloy fine particles, Ag fine particles, Ag alloy fineparticles, Ca fine particles, Ca alloy fine particles, Zn fineparticles, Zn alloy fine particles, Zr fine particles, Zr alloy fineparticles, Al fine particles and Al alloy fine particles.
 4. A systemfor producing high-pressure hydrogen, comprising: a hydrogen generatorinto which water and a hydrogen-generating material which reacts withwater to generate hydrogen are introduced, said hydrogen-generatingmaterial and said water being weighed so that hydrogen having a targethigh pressure is produced; a hydrogen-storing vessel for storing ahigh-pressure hydrogen generated by said hydrogen generator; and aconnecting member adapted to connect said hydrogen generator and saidhydrogen-storing vessel to each other in a course of filling saidhydrogen-storing vessel with the high-pressure hydrogen and adapted todisconnect said hydrogen generator and said hydrogen-storing vessel fromeach other after said hydrogen-storing vessel is filled with thehigh-pressure hydrogen.
 5. A system for producing high-pressure hydrogenaccording to claim 4, wherein said hydrogen-generating material is atleast one selected from among NaH, Na, NaBH₄, MgH₂, Mg, Mg(BH₄)₂,Mg(AlH₄)₂, LiH, LiAlH₄, LiBH₄, Li, K, Ca, Sr and Be.